Imagine red blood cells as the subway system of your blood. They transport oxygen and nutrients to various locations in your body, making their role vital to your health. Your body relies on the correct proportion of red blood cells for you to stay healthy.
If your physician suspects you have too few red blood cells, a hematocrit or Hct test may be ordered. This simple blood test can reveal the proportion of red blood cells in your blood.
If your physician orders a complete blood count (CBC) test, the hematocrit test is included. Other tests in a CBC are a hemoglobin and reticulocyte count. Your doctor will look at your overall blood test results to gain an understanding of your red blood cell count.
A hematocrit test can help your doctor diagnose you with a particular condition or it can help him or her determine how well your body is responding to a particular treatment. While the test can be ordered for a variety of reasons, it’s often used to test for anemia, leukemia, dehydration, or dietary deficiencies.
Let your doctor know if you have undergone a blood transfusion recently, as this may affect your results. Pregnancy also can decrease your blood urea nitrogen (BUN) levels due to increased fluid in your body. If you live at a high altitude, your hematocrit levels tend to be higher due to reduced amounts of oxygen in the air.
A medical provider will need a small sample of blood to test your hematocrit. This blood can be drawn from a finger prick or taken from a vein in your arm. Blood will collect in a slim vial known as a pipette or in a larger tube.
Gentle pressure may be applied to the puncture site, and you may need a bandage if the area continues to bleed. You can typically resume everyday activities after testing.
The laboratory test for your hematocrit is performed using a centrifuge, which is a machine that spins at a high rate to cause the contents in your blood to separate. A laboratory specialist will add a special anticoagulant to keep your blood from clotting, allowing it to separate.
When the test tube is taken out of the centrifuge, it will be settled into three parts: red blood cells, anticoagulant, and plasma or fluid in your blood. Each will settle at different parts of the tube, with the red blood cells moving to the bottom of the tube. The red blood cells are then compared to a guide that tells what proportion of your blood they make up.
While the laboratory that tests the blood the sample may have its own ranges, generally accepted ranges for hematocrit depend on your gender and age. According to the Mayo Clinic, typical ranges are as follows (Mayo Clinic):
- Adult men: 38.8 to 50 percent
- Adult women: 34.9 to 44.5 percent
Children ages 15 and under have a separate set of ranges as their hematocrit level changes rapidly as a child ages. The specific lab that analyzes the results will determine that hematocrit range of normalcy for a child based on his or her age.
Low hematocrit levels can indicate:
- bone marrow diseases
- chronic inflammatory disease
- deficiencies in nutrients such as iron, folate, or vitamin B12
- internal bleeding
- hemolytic anemia
- kidney failure
- sickle cell anemia
High hematocrit levels can indicate:
- congenital heart disease
- dehydration kidney tumor
- lung diseases
- polycythemia vera
Your doctor will likely compare the results of your hematocrit test to the other parts of the CBC test and your overall symptoms before making a diagnosis.
A hematocrit test is not associated with any major side effects or risks. You may have some bleeding or throbbing at the site of the blood draw. Let your doctor know if you experience any swelling or bleeding that does not cease with a few minutes of pressure applied to the puncture site.